Statins are one of the most commonly prescribed medications in the United States and are used for the treatment or prevention of coronary artery disease. Muscle symptoms (pain, aches, weakness, or cramps) are the most common side effect associated with statin use and these symptoms affect quality of life and cause some individuals to stop using statin therapy. Some evidence suggests that use of a dietary supplement, coenzyme Q10, may improve muscle symptoms in statin users. Coenzyme Q10 (CoQ10) is an essential cofactor in mitochondrial energy production and has been linked to the development of neuromuscular diseases. Because CoQ10 shares a common biosynthetic pathway with cholesterol, it has been hypothesized that inhibition of CoQ10 synthesis by HMG-CoA reductase inhibitors (statins) may be responsible for adverse muscle effects experienced by some statin users. Serum CoQ10 has been shown to decrease with statin use, but it remains unclear if this has clinical significance. The applicant proposes two studies focused on statin use and muscle symptoms. First, the applicant proposes a rigorously designed randomized, double-blind, placebo-controlled, parallel-arm trial of 100 statin users with active muscle pain to evaluate the effects of CoQ10. From among ~300 patients who have a history of muscle pain with statin use, 100 patients who have confirmed active muscle symptoms on rechallenge with simvastatin 40 mg/day during a run-in phase of up to 3 months will be randomized to a standardized 600 mg CoQ10 supplement (300 mg taken 2 times daily) or placebo over 4 weeks. The primary outcome will be pain severity at 4 weeks. Secondary outcomes will include ability to tolerate simvastatin 40 mg/day and muscle strength. Second, the applicant will use data from the National Health and Nutrition Examination Survey to evaluate the relationship between pain burden and muscle strength with statin use in U.S. adults 40 years and older. Through the above research, coursework at the Harvard School of Public Health, seminars, and training in collecting standardized measurements of muscle symptoms, the applicant will enhance her methodological skills, gain experience in clinical trial research, and collect data for future studies as an independent investigator. The applicant's long-term goal is to become a leader and expert in research on dietary supplement use among individuals with cardiovascular risk factors or disease.